Manufacture of cadmium yellow pigments



Patented Aug. 27, 1946 UNITED STATES PATENT OFFICE MANUFACTURE OFCADMIUM YELLOW PIGMENTS i Ludwig Francis Nerlinger, Wilmington, Del.,as-

signor to E. I. du Pont de Nemours & Company, Wilmington, Del., acorporation of Delaware No Drawing. Application November 23, 1944,

Serial N0. 564,899

, 1 This invention relates to the production of cadmium yellow pigments,and more particularly to a novel improved method for obtainingzinccontaining cadmium sulfide pigments in lighter,-

usually contain casein as a binder which is solubilized with the alkali.The water phase of the paint is therefore alkaline and the pigment-whichis used must be alkali-resistant. Chrome yellow has been widely used forthe production of bright yellow paints but is definitely deficient inalkali resistance. Hence, it is not suitable for use in aqueous emulsionpaints. Hansa Yellow pigments are not satisfactory for use in suchpaints, due to the tendency of the pigment to migrate to the oil phaseof the paint.

Cadmium sulfide pigments range in color from orange to a greenishyellow. Their color depends, among other things, on the method ofcombining th reactants used in their production, the calcinationtemperature to which the pigment is subjected, and the amount of zincco-precipitated with the pigment. The orange shades can be prepared byco-precipitating cadmium sulfide andbarium sulfate from solutions ofcadmium sulfate and barium sulfide. Some variation in hue can beobtained by proper selection of operating conditions, but no knownmethod has eX- isted for obtaining the lighter and greener shades ofcadmium sulfide from pure cadmium sulfate solutions. Prior methods forobtaining such lighter, greener shades'involve the co-precipitation ofzinc and cadmium sulfides from a mixed A,particular bject of theinvention is aqueous, emulsion-type A further object is to provide anovel 5 Claims. (01. 106-301) method for precipitating and recovering animproved cadmium sulfide pigment. Additional objects of the inventionwill be apparent from the ensuing description of the invention.

The foregoing and other objects are obtainable in this invention whichcomprises first preparing a suspension of precipitated zinc sulfide andbarium sulfate and thereafter precipitating cadmium sulfide and bariumsulfate in the presence of and upon the surface of said suspended zincsulfide particles.

In practically adapting the invention, the precipitation reaction isconveniently conducted in a suitable reaction vessel, such as aconventional type tank, equippedwith a sweep agitator and to which thereactants, in solution, may be added as desired. To insure properagitation at'the start ofthe action, water'is first added to the tank.Thereafter, a solution of zinc sulfate (at a concentration ranging fromabout -450 g./l.) together with a chemically-equivalent amount of bariumsulfide, is added to the tank and until a slight reaction for sulfideions is obtained. Addition of the chemically-equivalent amounts of thesetwo reactants provides an aqueous suspension of raw lithopone pigment (aco-precipitated mixture of zinc sulfide and barium sulfate).-

After the adjustment of the end point to provide a slight test forsulfide ions, a solution of cadmium sulfate and a further quantity ofbarium sulfide are simultaneously added to the tank in order toprecipitate a cadmium lithopone composition upon the zinc sulfidelithopone already present in the tank. The cadmium and barium reactantsare added in equivalent amounts and While the pH of the solution ismaintained within a range of about 6.0 to 8.5 or approaching neutrality.The resulting precipitate, comprising cadmium sulfide, zinc sulfide andbarium sulfate,

is then adjusted to about 8.6 pH using barium sulfide solution, is thenfiltered, dried and calcined at a temperature ranging from about 600-750 C. to develop essential pigment properties, including oilabsorption, tinting strength, brilliance of color, etc. Y

To a more complete understanding of the invention, the followingspecific examples are given,

each of which i merely illustrative ofand not sulphate solutionanalyzing 400 gram of zinc sulphate per liter were placed in an agitatedtank. and to this was added sufficient 20 Baum barir 3 I i um sulphidesolution to give a slight excess of resorted to herein, the quality ofthe resulting sulphide ions. To the resultant slurry a cadmiproductdemonstrates the existence of a clear um sulphate solution analyzing 97grams cadadvance in the art, the resulting pigment being mium per literwas added in a small stream while eminently suited for use in aqueousemulsion simultaneouly adding an equivalent amount of 5 paints whereinalkali resistance and brilliance barium sulphide .as a 20. B.solution... This 51-, of colorlare ofprime importance.v

multaneousracldition was continued until 'Z50rvol- Wi-l'ileia-zincsulfide or'zinc sulfide-containing umes of cadmium sulphate solutionwere added precipitate comprises a preferred type of mateand whilemaintaining the pH at approximately... rial upon which the cadmiumsulfide is pre- '7.(). At the end of the addition of these re-'cipitated, other insoluble zinc compounds, such agents, the end pointwas adjusted: to; 8;6.' pH- ass-the? oxide, carbonate, silicate, orphosphate, f and th suspension filtered, dried and calcinedlfl may besusp n in q e m dia for intimate at a temperature of 700 C. with theusual pre.-. c ion withv the cadmium sulfide subse cautions to preventoxidation duringicalcinationi qu y pit d n sa d s p n i n- T ese Theresulting pigment was compared? ,withlai L115, Zinc materials need notbe prepared in the reacpigment produced by the same amount of the tiontankused for the precipitation of the cadf in accordance with the"priorart.

, amount'ofthe'reagents; Because of the smaller,

I reagents but by adding the zincisulphatezsolutionr miunrlithoponaib tm y e p ecipitated in a V 7 i to the cadmium sulphate solution prior topre -l separate vessel if it is found more convenient to 1 cipitation.The first sample returned thetsame. do so.. Thus, in the case of the useof zinc lithohue as the second sample,.but exhibited definitely poneas'a starting material, raw zinc lithopone superior brilliance of color,having a brightness liquorfrom normal z nc li h p n per ions value(in.;%, reflectance) of 7315, as comy c nveni ntly d. In the pr ctice ofparedwith a value of 71.9 for aproductiobtained" the invention,howeverflit' s, ne s ary and sential that the insoluble zinc compound be5 present at the start of the react-ion,'in order that Example H thecadmium lithopone can be effectively pre- 1 400* volumes of water and-55volumesof a zi'no cipitated upon and intimately associated theresulfatesolution ana1yzing= 400 grams" of" Z'nOs with. Mere-addition of theinsoluble zinc comper liter were placed inan agitatedtanli andpound to asuspension of precipitated cadmium sufiicient 20 Baum barium sulphidesolution-e lithopone, followed by-filtration, drying andcal- 1 was runin to givea slight excess of'su'lphideions; h cination, will not yieldthe-superior product ob- 7 To the resultant slurry 750 volumes of acadtalliedby a pr ct ce of h v n o r I .Wi,1l.

mium sulphate solution containing QV-graa'ms the c0- -precipitation ofthe zinc sulfide with the cadmium per literwas added in a small streamcadmium; as contemplated in priorpractice, yield while; simultaneouslyadding an equivalent f apigment exhibiting superior brillianceof coloramount of'barium sulphide solution to maintain possessed by the productof this invention.

j the pH at approximately 7.0. At the end of -the The brightness valuesreferred toherein were addition of these reagents the end point-wa -ad fdeterminedby-rwell-known tests invo v n the justed to 8.6 pH and thesuspension filtered prepa at o -of a paste of ther m n in oilfand' The.precipitate was then dried and calcined at; 4o a i gusing a nter ectometer a temperature' of7d0C. 7 and with a, green light filter.

1 A, similar pigment was prepared by addingithex as my inv n ion:

zinc sulfate solution to the cadmium sulfate p s p u ing an improvedcad-1 solution prior toprecipitation, using the; same; mium sulfide pigmentwhich'comprises; precipitating cadmium sulfide by reacting sulfate withba'riumsulfide inthe presencev of an aqueous ratio of zinc to cadmium,these pigments; were,

slightly'lessgreen than the pigments of Examp'lel y s spen i n f r w liop p ment; con- I.I However, the sample prepared according-to; sistn Ofa(BO-p p l fe fi e tliisinventiongwas a ain found to e hibit deii=- d a msulfate, a t recovering andca Y .nit'el'y superior brillianceof color,givinga bright Ciriing the resulting" zinc-rco ta m m nessavalue'of 6913ascontrasted with-a valuegof" s fi e pr duct" at a t mperature ran ingfrom 642.8 for theprior art product; p 600-750? C. p V The order ofaddition of the various reagents ss r producing animproved cad: in theinvention'has'been found to be quite'immium s l e pi m nt whichcomprises p e' me portant inand critical to the productionof tatin-gcadmium lithopone in the presence of zinc,

brilliant and uniform colors in accordancewith' lithopone ySimultaneously/adding to a 5118- the invention. As outlined above, thezinc pended aqueous slurry of S nC t oponc 3 sulfide is firstprecipitated and suspended in sol'utionsof cadmium sulfatev and bariumsulfide, aqueous slurry, following which precipitation of and thenrecovering and calci ng the resulting.

the cadmiumsulfide is effected. This order of (13 cadmium lithop ne pgment.v

precipitation is essential and critical to theiin- 3. A process forobtaining a p oved cad.- vention and has been found necessary in 010-mium sulfide pigment which comprises. initially ta-iningthe markedimprovements which the suspendingraw lithopone pigment consisiting of 1present: invention affords; especially over the V a co-pre'cipitatedmixture of zinc. sulfide. andv prior art method of co-precipita-tion,wherein 65 barium sulfate, in an aqueous slurry,. and there- 3 the zincand cadmium sulfate solutions have after simultaneously adding tothe-resulting, susbeen combined; before the precipitation takes pensionsolutions. of cadmium sulfate and barium place- Therefore, it will beunderstood that the sulfide, in order to precipitate cadmium lithe-Vimproved method'of this invention comprises the I p one upon saidsuspended raw lithoponaand j precipitation of cadmium lithopone-in thepres- 7 then recovering. and calcining the resulting zinc.- ence of zinclithopone by: used the simultaneous containing cadmium sulfide product."7

addition of the cadmium sulfate and barium V 4. A process,- forobtaininganr improved cad: sulfide reactants to azinc lithopone slurry.mium. sulfide. pigment which comprisesreacting While it vi's not fullyunderstood why. thefunexe cadmium sulfate. with barium sulfide in an 7peoted results accrue by reason of the procedures .75 aqueous/slurry.suspension of an, insolublein;

organic zinc compound to precipitate cadmium sulfide upon said suspendedzinc compound, and then recovering and calcining the resultingzinccontaining cadmium sulfide product. 7

5. A process for obtaining an improved cad mium sulfide pigment whichcomprises reacting cadmium sulfate with barium sulfide in an aqueousslurry suspension of zinc sulfide to precipitate cadmium sulfide uponsaid suspended zinc sulfide, and then recovering and calcining theresulting zinc-containing cadmium sulfide 6 product.

LUDWIG FRANCIS NERLINGER.

Certificate of Correction Patent No. 2,406,472: I August 21, 1946.

I LUDWIG FRANCIS N ERLIN GER It is hereby certified that errors appearin the printed specification of the above numbered Jpatent requiringcorrection as follows: Column 2, line 18, for action read reaction;column 3, line 28, for Z110 read ZnSO column 4, line 45, claim 1, beforesu1fat'e' -insert cadmium; and line 63, claim 3, for consisiting readconsisting; and that the said Letters Patent should be read with thesecorrections therein that the same may conform to the record of the casein the Patent Office.

Signed and sealed this 29th day of October, A. D. 1946.

LESLIE FRAZER,

First Assistant Oomxmz'ssz'oner of Patents.

